Many modern vehicles include radar scanning systems to assist the vehicle in such applications as automated emergency breaking (AEB) to stop the vehicle when objects are detected in a given vehicle's path. Traditional non-scanning radar transmitters illuminate the entire system field of regard (e.g., area where objects are to be detected) where associated receivers then detect backscatter from objects in the field of regard. Since the entire field of regard is illuminated, the transmitted energy is spread across the entire field of regard. A scanning phased array with a narrower beam illuminating a narrow field of view (e.g., angular cone) within the field of regard will have the same transmitted energy concentrated in a smaller beam, resulting in higher energy density and higher levels of return.
In order to cover the entire system field of regard, the narrower beam produced by a phased array beam forming network must be electrically scanned across the system field of regard. The phased array transmit beam illuminates each region for a brief period of time, then repositions to a new position and illuminates this second position, continuing until the entire system field of regard has been illuminated. The array transmit beam then cycles back to the starting position and repeats. Typical operation is to scan successive adjacent regions at a fixed scan rate, starting on one edge of the instantaneous field of view, moving the beam such that the edge of the beam slightly overlaps the previous field of view, and so on until the entire system field of regard has been illuminated. Adaptive scanning techniques may have the beam interrogate areas with known objects more extensively.
In a scan time example, assuming a frame rate of 20 frames per second (FPS), each field of regard should be sequentially illuminated within 50 msec. With azimuth only scan, with field of regard of 60 degrees, and field of view at 6 deg, the dwell time is about 5 msec at each beam position in the field of regard. The minimum dwell time at each beam position is governed by system accuracy requirements. Wider fields of regard reduce the dwell time at each position. As dwell time decreases, the amount of data collected at each field of view position within the field of regard decreases, which can decrease the accuracy of a system. Larger fields of view allow for longer dwell times and increased data collection, but transmitted power is spread over a larger beam area, which may reduce sensitivity of the system.